There are many articles and sources that expose the many schemes that auction houses have and have allegedly participated in over many years (selling through auction is a very old practice).
To be fair I encourage you to read all the comments in the article, I provide a link to, and beware that there was no prosecution in that particular case. The author retracted after BJ threatened lawsuit. But, as the commenters correctly point out, a retraction does not mean the allegations are untrue. A simple Google search on auction schemes will result in some eye opening information if you think it is all on the up and up.
As to actual, confirmed, selling prices it takes some time and some detective work is required but I have found that well established sources such as Edmunds, Hagerty, Kelly use pretty good intelligence (based on actual replacement costs as established by insurance companies) to establish value models. Other than that the best bet is to gain confirmation, such as we have on this particular car, that the reported selling price is accurate and the buyer took delivery.
Comments were not directed at you personally since I have absolutely no idea what you do with your information. I am simply making a general observation that there are a huge amount of buyers and sellers out there that try to establish fair market value from asking prices and unconfirmed sell prices.
I think at this juncture we'll have to agree to disagree. I think that most of the transactions that clear both on ebay and auction sites represent real transactions and, therefore, are somewhat useful info. You feel that when they are unconfirmed by a separate source, they are completely useless. Got it. Finis.
But to my original point regarding the particular auction in this thread, the bid (from ebay ad) and ask price (from the online ad) were so far apart ($12K - $40K) that there was "no market here" for this transaction. And if the seller was shilling bids on his own car the outcome was even stranger.
Re: "Comments were not directed at you personally..."
Good, I was concerned.